Mobile terminals, and especially mobile telephones and headsets, are becoming increasingly smaller. These terminals require a radiating element or antenna for radio communications. Conventionally, antennas for such terminals are attached to and extend outwardly from the terminal's housing. These antennas are typically retractably mounted to the housing so that the antenna is not extending from the housing when the terminal is not in use. With the ever decreasing size of these terminals, the currently used external antennas become more obtrusive and unsightly, and most users find pulling the antenna out of the terminal housing for each operation undesirable. Furthermore, these external antennas are often subject to damage during manufacture, shipment and use. The external antennas also conflict with various mounting devices, recharging cradles, download mounts, and other cooperating accessories.
Application Ser. No. 09/189,890 describes an internal loop dipole antenna for a cellular telephone. The antenna includes extra traces and tuning elements on the same physical plane as the antenna element to enable dual-band operation. As phone designs become increasingly smaller and the antenna is brought closer to the ground plane (PCB) of the phone, the antenna begins to lose its effectiveness. It has been discovered that the effective bandwidth of the antenna is narrowed as the antenna is brought closer to the ground plane of the antenna. Also, tuning of the resonance frequencies becomes problematic due to the strays and parasitics caused by the antenna's close proximity to the ground plane. The extra traces and tuning elements did not provide sufficient bandwidth in both bands of operation. Also, lumped elements such as capacitors and inductors did not adequately eliminate the strays and parasitics.
Accordingly, there remains a need for a dual band antenna that will operate effectively in two distinct operating bands even when the antenna is brought in close proximity to the ground plane of the phone.